For example, a three-way valve includes a valve housing having an inlet port, an outlet port, and an exhaust port. Fluid is supplied into the three-way valve through the inlet port. The three-way valve distributes the fluid through the outlet port. The three-way valve partially exhausts the fluid to a low pressure component through the exhaust port. The valve housing is inserted into an insertion hole. The valve housing and the insertion hole define an annular gap therebetween. The annular gap is sealed using multiple O-rings. The multiple O-rings are supported by the outer circumferential periphery of the valve housing.
According to U.S. Pat. No. 6,378,840 (JP-A-2001/82625), the valve housing is molded of resin for reducing manufacturing cost of the valve housing in a complicated shape. The valve housing has a valve seat. The valve seat is made of metal for producing strength. Components of the valve housing other than the valve seat are molded of resin for forming the complicated shape. In general, mechanical strength of resin is lower than mechanical strength of metal. Accordingly, when excessive force is applied to the valve housing, the resin components constructing the valve housing may crack. Consequently, oil may leak to the outside.
When the valve housing is formed of metal, reliability of the valve housing can be enhanced against external force. However, it is necessary to secondarily apply machining work to the outer circumferential periphery of the metallic valve housing for undercutting O-ring grooves. Accordingly, manufacturing cost of the valve housing increases.
Alternatively, it is conceivable to provide a base metallic member as an interior of the valve housing, and to provide an outer resin member as an exterior of the valve housing having a complicated shape defining the O-ring grooves.
However, the thermal expansion coefficients of the outer resin member and the base metallic member are different from each other. Accordingly, in this structure, when the valve housing is exposed to cool and hot environment, a gap may arise in the boundary between the outer resin member and the base metallic member, which tightly make contact with each other. When a gap arises in the boundary, fluid may leak to the outside through the gap. When excessive force is applied to the valve housing, the outer resin member, which is lower than the base metallic member in mechanical strength, may crack, and fluid may leak to the outside through the gap.